1. Technical Field
The present invention relates in general to an improved disk drive pivot sleeve, and in particular to an improved disk drive pivot assembly with a locally deformable sleeve.
2. Description of the Related Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, two or three disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
The only other moving part within a typical HDD is the actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions (air bearing design) on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter""s surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.
Actuator assemblies typically utilize a comb-like structure that are formed from very stiff materials in order to increase servo bandwidth. These classes of materials, such as ceramics, metal matrix composites, and beryllium alloys, are up to five times stiffer and five times harder than aluminum. One common means to attach a pivot to a comb is to use a small screw to either push or pull the pivot into a scalloped portion of the comb bore. Due to slight geometrical imperfections (tolerances) of the pivot and comb bore, the parts do not make ideal and uniform contact. Fortunately, the elastic nature of aluminum comb bodies and pivot sleeves allow them to locally deform a small but sufficient amount at the points of contact, thereby effectively distributing the loads evenly among lines of contact.
Problems arise when a stiffer comb body does not locally deform against the pivot bearing sleeve, thus causing non-uniform loads at the lines of contact. The problem is exacerbated when the pivot sleeve is also made of the same high stiffness material in order to match the coefficient of thermal expansion of the comb and it can no longer locally deform against the comb bore. When this condition exists, the actuator is dynamically unstable because the comb and sleeve oscillate slightly with respect to each other under seek conditions. Seek energy causes the comb to rock on the pivot at the points with the highest loads. This instability will cause track misregistration at current and future track pitches. Thus, an improved disk drive pivot assembly is needed.
One embodiment of an improved disk drive pivot assembly has a locally deformable internal sleeve. The sleeve is equipped with two small deformable zones where the sleeve makes contact with the actuator comb bore. The zones can be in the shape of two rings with a rectangular or circular cross-sectional shape. The material may include zinc, magnesium, copper, or aluminum, or their alloys. These materials are relatively soft and have a relatively low stiffness compared to the comb bore. The thickness of the rings may range from approximately 0.25 to 1.0 mm, and they may be attached via shrink fit or adhesive bonding.